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Windows 8 Release Preview Is Out – Let’s Talk Security

I could take screenshots and do a full review of the Windows 8 OS but some other blog that gets paid to do reviews would just do it better so I’ll stick to what this blog is for – security.

Windows 8 has officially been released as a Release Preview, meaning that just about everything you see in this RP is what you’ll see in the final release. The biggest changes in Windows 8 are pretty surface – the highlight is an entirely new Metro UI, which features a full screen start page and various other major UI changes. There are also some big changes under the hood – Windows 8 is a lighter, faster OS than 7 with lower RAM usage and improved multicore support. And then there’s security…

ASLR

Address Space Layout Randomization (ASLR) is a mitigation technique first designed by PaX foundation. The idea is to randomize a programs address space (the range of virtually memory addresses that make up a process) in order to prevent Return Oriented Programming (a technique used to bypass Data Execution Prevention.) Essentially, because the attacker does not know where areas of the address space are they are unable to make use of that address space in a way that would otherwise allow further compromise of the system.

ASLR relies on the attacker not being able to guess the location of address space. They only have three real options (in terms of defeating ASLR):

1) Find part of the address space that isn’t ASLR enabled

2) Make use of information leaks

3) Bruteforce through the addresses

Windows 8 attempts to directly address (1) and (3.)

/FORCEASLR

In Windows 7- if I run a program like Firefox*, which is ASLR enabled but I use Norton Toolbar, which isn’t ASLR enabled I basically defeat the purpose of ASLR because there’s a predictable address. Windows 8 address this with /FORCEASLR, a compile time flag that will force the entire address space to be ASLR enabled (oversimplification, not entirely true, good enough.)

The benefits are obvious, simply using the /FORCEASLR flag in your program means that no other program will significantly degrade the effectiveness of ASLR.

*Firefox has actually solved this issue by forcing toolbars to use ASLR. It’s an outdated example but it works.

Improved Randomness

ASLR effectiveness necessitates the inability of an attacker to guess or predict locations of address space. If there isn’t sufficient address space or there isn’t sufficient entropy the ASLR won’t be effective and an attacker can bruteforce their way to a useful area.

Windows 8 has improved the random number generator and thereby increased randomness in ASLR.

For 32bit systems this is important. Virtual address space on a 32bit system is much smaller than that of a 64bit system (addressable space on 32bit is 2^32 as opposed to 2^64 for 64bit) so bruteforcing is much easier. Improved randomness will make this more difficult – though because of the small address space it’s potentially a lost cause.

Guard Pages

Guard pages work to prevent usable buffer overflows. Developers can make use of Guard Pages to protect areas of address space – when an attacker tries to overflow an area protected by Guard Pages, they’ll end up throwing an exception.

AppContainer

There aren’t a lot of details about AppContainer yet but it looks like Windows is finally getting proper Mandatory Access Control. The ability to apply finely grained application MAC is hugely beneficial both to preventing and limiting exploitation.

Programs don’t have to squeeze into low integrity anymore, they can use whole-process sandboxes (which aren’t actually better, just easier) to segregate themselves from the system.

The jury’s out on this feature. If it’s as powerful as AppArmor I’ll be happy.

Internet Explorer 10 Metro

IE10 Metro runs in the new Metro environment (WinRT) and is sandboxed from the rest of the system. It also contains a built in Flash player, which Microsoft has integrated into the browser for improved stability, security, and performance. A smart move on Microsoft’s part as the Flash player is still necessary for viewing a ton of the internet and it is also one of the most commonly exploited applications.

Internet Explorer 10 Desktop

The desktop IE10 (and this applies to Metro) will make use of all of the new security mitigations like FORCEASLR and improved randomness. IE10 will also include an “Enhanced Protected Mode”, which implements a further least-privilege mode based on the earlier Protected Mode principals.

The enhanced protected mode continues IE’s least privilege model, which is great and it should prove more difficult to break out of.

Full System Smart Screen

Smart Screen is an application reputation and heuristics system. Previously it was built into IE9 and an NSS Labs report noted it blocking 96+% of malware (there isn’t enough research on the effectiveness, take that report with a golf ball sized chunk of salt.)

SmartScreen in Windows 8 is now system wide. If an application hasn’t been seen before by MS you get a little message saying “hey, we haven’t seen this before, be careful.”

Personally, I don’t like it and I don’t think it will be effective. That’s just me. I don’t think users are capable of making decisions based on information like that and it threw me a ton of “false positives” (not actually FPs as it’s not calling it malware, same principal) so my trust in its opinion of software is seriously diminished. It won’t be effective for the same reason an AV that throws false positives isn’t effective – if I can’t trust the product I’ll never know when it’s right or wrong.

We’ll see.

SecureBoot

SecureBoot is a much reviled feature as everyone though MS would be locking Linux out of Windows 8 hardware. As I posted about earlier Fedora is already working on implementing it. SecureBoot prevents untrusted code from running before the OS. This will prevent rootkits from bypassing full disk encryption and/or wedging themselves deep into the operating system. It’s a great security feature and I think it will be very effective.

Microsoft Security Essentials

MSE is a widely used antivirus known for being pretty light and quiet – no false positives. It provides pretty decent detection ~50% when out of date and making use only of heuristics (most people probably don’t stay up to date) but I think we can expect that to fall.

As MSE has gotten more popular it’s also started to drop in performance. This is the case with any popular program. The first thing a hacker will do with their payload is test it against a number of antiviruses (automated tools exist for this) and if it passes by MSE but maybe Panda catches it they might release it anyway because MSE still makes up a huge part of market share.

Windows 8 will increase that market share and increase how seriously hackers take bypassing MSE. It’s detection, not preventative, so it’s flawed in that way.

Did I Miss Anything?

I’ve probably forgotten something. If so, leave me a comment.

All in all, Windows 8 is significantly more secure than Windows 7. If AppContainer turns out well it’ll be a huge boon. Even without AppContainer the numerous memory protections added as well as SecureBoot put Windows 8 far ahead of 7 and I’m excited to see Microsoft really taking security seriously. Personally I still feel safer on Ubuntu thanks to being able to do this but it makes Windows feel way more viable and competitive.